How would we know that it's really you casting your vote, and that someone isn't physically forcing you to vote in a certain way? We now have fingerprint sens

How would we know that it's really you casting your vote, and that someone isn't physically forcing you to vote in a certain way? We now have fingerprint sensors on the new phones. I can imagine, this will be a standard feature in 3-5 years. Back to your question: This could also happen with "regular" voting.